This invention relates to a method of numerical control, and to a numerical control device. More particularly, the invention relates to a numerical control method and to a numerical control device that enable a machining operation to be interrupted when a specified signal, such as an abnormality signal indicative of tool breakage or the like, is generated during the machining operation, and that enable numerical control processing to be executed in accordance with the specified signal so that machining can be resumed following such processing.
When an abnormality such as a broken tool develops during a machining operation being performed under the control of a machining program, the operator ordinarily halts the machining operation immediately, feeds the broken tool manually to a prescribed tool changing position without allowing the tool to contact the workpiece, and then changes the tool. Machining then resumes from the beginning of the machining program. Alternatively, the operator may reposition the new tool at the point where the original tool broke and then allow the machining operation to resume from that point. Since this procedure requires the intervention of human labor, a considerable amount of time elapses from the occurrence of the abnormality to the resumption of machining. The procedure is also complicated. Moreover, when an attempt is made to accomplish the foregoing automatically, a considerable amount of additional hardware must be provided.
Already known in the art is a numerical control device having an automatic tool change function, the device being adapted to transport a tool automatically to a tool change position, change the tool and then resume machining (as disclosed in, for example, Japanese patent application No. 48-86628 filed on Apr. 4, 1975 and the FANUC 200C operator's manual, on pages 59 to 63, published by FUJITSU FANUC, LTD., June 1980). However, the known numerical control device having the tool change function will not execute automatic tool change processing unless it is instructed to do so by the machining program. In other words, a tool change will not take place in the event of an unexpected event such as the breakage of a tool during machining.